Activity of the enzyme g-glutamyl transpeptidase (g-GT) (EC 18.104.22.168) a putative facilitator of amino acid (AA) transport in the mammary gland, increases before lactation and decreases at weaning, suggesting a role in AA transport for milk protein synthesis. The effect of g-GT inhibition by acivicin and supply of cyst(e)ine from N-acetylcysteine (NAC) on mammary AA uptake and milk production was studied in lactating goats. NAC increased (P<0.05) arterial supply of some AA but did not increase arterio-venous difference as a percentage of arterial supply (extraction %) and did not alter milk protein yield. Acivicin decreased (P<0.05) milk protein yield but this effect was not found when NAC was administered in combination with acivicin. This indicates that NAC, by indirectly enhancing intracellular cysteine, countered the effect of acivicin inhibition, suggesting a role for g-GT in supply of cysteine for milk protein synthesis.
Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 244-247, 2001
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